This invention relates to communication facility checking systems and in particular to an arrangement for checking the integrity of switched communication paths to reduce customer service irregularities due to faulty or inoperative conditions thereon.
In the prior art, telephone calls to directory assistance operators were frequently routed from a fully automatic switching office via a trunk to a destination office equipped with directory assistance operator positions. The establishment of such a connection customarily did not require call address outpulsing. In these arrangements, the common control equipment at the fully automatic office would be released from the connection immediately after the equipment had exchanged cross-office signals with its appropriate outgoing trunk circuit to the destination office. While this signal exchange was effective in verifying the integrity of the cross-office channel at the fully automatic office, the release of the equipment immediately thereafter had the disadvantage of leaving a calling party in the "high-and-dry" condition, i.e., without an audible supervisory response, whenever a carrier outage or other failure had occurred on the interoffice trunk between the outgoing trunk circuit and the operator-assisted office.
Recent trends towards the centralization of directory assistance operators at relatively remote suburban locations, coupled with the more widespread use of the automatic call distribution system for reservation and order taking have caused a proliferation of connections to operator positions. Consequently, the relocation of operator positions onto call distributor switching entities has intensified the need for an integrity check of the entire connection, including the interoffice portion. Thus, early directory assistance switching arrangements have not been equipped to solve "high-and-dry" network performance problems and later developements in the placement of operators have more greatly aggravated the problem.
In certain prior art systems integrity checks are performed on calls requiring outpulsing and the check is incidentally derived during the call setup sequence. This sequence requires that the common control circuit await a "start-outpulsing" signal from the facilities at the destination office. If this signal is not received within a predesignated time interval, timeout circuitry causes the common control circuitry to reattempt the completion of the call over a different outgoing trunk circuit or, if that fails, to connect the calling party to a reorder signal.
The foregoing integrity check is, however, not readily applicable to call processing systems in which no call address outpulsing is made such as when a call is to be completed to an operator position, because, in such systems no "start-outpulsing" signal is used. In order to check the integrity of such a "non-outpulsing" connection, it would be desirable and necessary to delay the release of common control equipment at the fully automatic office until the interoffice integrity check can be completed. The apparent solution of modifying the common control equipment itself by providing for its delayed release and for direct supervision by this equipment of the entire connection including the interoffice position, as is done on calls that do require outpulsing, has two disadvantages. First, the common control equipment changes would have to be extensive so as to be capable of distinguishing among the various subclasses of trunks that are used on "non-outpulsing" calls. For example, the common control unit would have to distinguish between connections to reorder trunks that require no integrity supervision because the trunk employed appears directly at the switch of the fully automatic office and connections to interoffice trunks which, in turn, connect to call distribution destination offices that do require the integrity check. In addition, common control equipment modification would entail the retrofitting of hundreds of common control circuits at all fully automatic offices, thereby entailing great expense.
In view of the foregoing, it is apparent that no facilities were heretofore available for checking the integrity of an interoffice communication path where no outpulsing was utilized in the call processing. A need therefore exists for an arrangement that prevents calling party annoyance and confusion when the switching system does not respond to the caller efforts and does not return an audible call disposition signal because of a trunk outage or a common control equipment failure at the destination office. It is also desirable to provide equipment that verifies interoffice trunk integrity without resorting to costly common control equipment modifications or to changes that affect even those subclasses of "non-outpulsing" call connections which do not require an interoffice integrity check because of their direct termination at the office switch.